The work proposed for the year l977-78 consists of three simultaneous phases. First, continued studies of fluorescent-dyed hygroscopic aerosol deposition will be conducted in a sophisticated physical model of five generations of the human bronchial tree. The physical model includes the temperture, humidity and oscillating flow conditions present in the real bronchial tree as well as the proper bifurcation geometry. Second, studies will be started on dyed hygroscopic aerosol deposition in the lungs of mongrel dogs. Third, work will be started on the development of a finite element computer model to predict hygroscopic aerosol deposition patterns in real human lungs, taking advantage of the information gained from the first two phases mentioned above. These three phases will be carried out simultaneously in working toward the final goal of providing recommendations for the optimization of hygroscopic aerosol delivery systems in patients.